A heating device for a domestic electrical appliance is, for example, known from European patent EP 421 442 B1. In the latter portion, a description is given of a drum washing machine having a heating device, which is passed through the wall in the lower area of an outer tub. The passage point of the heating device in the wall is sealed by means of a holder of the heating device.
European patent application EP 633 342 A1 for example discloses a method and a device for optimizing detergent use. A device for determining the conductivity is for this purpose installed in the water supply line of a washing or rinsing machine and establishes the conductivity of the water. The water conductivity changes as a function of the ions dissolved in the water or the degree of calcification. The conductivity of the cleaning liquid cannot, however, be determined with such a method or device.
Therefore the problem to be solved by the invention is to provide a heating device permitting a further optimization of the detergent requirement in an automated cleaning process as a result of improvements to the measurement and in particular there is to be a better adaptation to the cleaning process. Water and time are saved and the washing or laundry is washed more carefully or gently. Simultaneously, the invention aims at reducing the working steps in installing the measuring systems.